Hydrocarbons can be converted to fluorocarbons in two commercially viable ways. Electrochemical fluorination (ECF) is widely used to fluorinate materials which are soluble and stable in liquid hydrogen fluoride (HF). Of among the classes of materials prepared in this manner, perfluorotertiary amines and perfluorosulfonic acids are best suited for the technique giving yields generally in excess of 70%. Other classes of compounds such as carboxylic acids and their derivatives can be fluorinated electrochemically; however, the yields are usually low and have a tendency to decline rapidly as the number of carbons in the molecule is increased. In general, a very low yield (less than 25%) will be obtained for any perfluorinated carboxylic acid containing over 12 carbon atoms.
A second widely used process for preparing perfluorocarbons involves contacting a hydrocarbon, in the gaseous form, with cobalt trifluoride. This technique, although narrow in applicability, works well for low molecular weight hydrocarbons, especially polyaromatic compounds which are sufficiently volatile to allow vaporization. Examples of materials which can be fluorinated in this manner include decalin, tetradecahydrophenanthrene, naphthalene, decane, dodecane, etc.
Russell et al. (U.S. Pat. No. 3 897,502) describe a process whereby one or several fluorine atoms can be added to a partially fluorinated low molecular weight hydrocarbon. The material to be treated is dissolved in an inert solvent through which dilute fluorine is bubbled at low temperatures (-10.degree. C. to -30.degree. C.). The resulting product is a partially fluorinated material which typically contains several additional fluorine atoms. Scherer et al. (U.S. Pat. No. 4,686,024) teach a method for perfluorinating low molecular weight partially fluorinated hydrocarbons. Highly fluorinated starting materials are slowly pumped into a fluorocarbon solvent over a 3 to 5 day period. As the organic material is being delivered, a large excess of pure fluorine gas is bubbled through the solvent (typically a 5 to 8 fold excess). An ultraviolet lamp is used to activate the fluorine to produce the products of interest. The yields reported generally range from 20% to 50% for materials which contain 3 to 5 hydrogens which must be replaced by fluorine. Calini et al. (European Patent Application 269,029) describe a fluorination process in which a hydrogenated ether compound is reacted with F.sub.2 diluted with an inert gas in a liquid phase, in the presence of 2 alkali metal fluoride.